The present invention relates to the field of electroacoustics and may be used in loud-speaker constructions for high-quality reproduction of music and voice in domestic conditions as well as in public-culture and professional audio reproduction systems, specifically in sound control channels, station announcement systems, transport means cabins and other places where an improved articulation is required, particularly in conditions of noise pollution and interferences.
Loudspeakers having a direct radiating electrodynamic driver (EDD) installed at the outer surface of the driver enclosure cabinet are well known and most widely used (see V. K. Iofe and others, HandBook of Acoustics, Moscow, xe2x80x9cSvyazxe2x80x9d, 1979).
Disadvantages of said devices, namely insufficient details and articulation of sound re-production, abrupt relationship between sound volume and distance R to EDD (by inverse-square law 1/R2), are associated to considerable dominance of a reactive (vector) component of their radiation over a necessary active (scalar) component.
These disadvantages are successfully overcome in a counteraperture loudspeaker comprising a module having a pair of identical, coaxial and inphase-counterradiating electrodynamic drivers transforming an electric signal into acoustic one at least in the middle-frequency part of the acoustic frequency range (see the International Application WO 95/05057, IPC6 H04R5/02, 1995).
In said counteraperture loudspeaker, the active components of the counterdirected radiation of the identical electrodynamic driver pairs are added together while the vector components are mutually subtracted and thereby compensated.
Disadvantages of such devices are requirement of paired number of the electrodynamic drivers having identical characteristics in the pairs and enlarged loudspeaker dimensions due to the interaperture space volume.
The main object of the present invention is to provide such loudspeaker construction which, on the one hand, would ensure high-quality sound reproduction by reducing the reactive component of the loudspeaker radiation and the parametric distortions (Doppler effect), associated to said component, and on the other hand, would not require use of pairs of identical band electrodynamic drivers, at the expense of that could be more compact and more simple to manufacture and adjust thereby would have relatively low manufacturing cost.
The basis for the present invention is the principle of operation of a counteraperture loudspeaker as well as the physico-mathematical idea of that the symmetry plane of given counteraperture loudspeaker, which is perpendicular to the common axis of the radiating apertures, is a plane of mirror symmetry. Symmetry is herein taken to mean not only a constructive symmetry, but also symmetry of dynamic of physical processes taking place at operation of the loudspeaker. Therefore, if any reflector overlapping the area of interaction of the vector, or velocity streams radiated by the electrodynamic drivers of the counteraperture pairs is placed in said plane, neither physical phenomena nor a degree of their development during the loudspeaker operation will not vary. Thus, a counteraperture loudspeaker having a reflector located in the above-mentioned plane may be formally represented as a pair of coaxial, counter-disposed, independent semicounteraperture loudspeakers, each of which is an independent module, all radiation aspects of which have full complex of unique positive properties of the counteraperture loudspeaker and which is more compact and less materials-intensive by comparison to the counteraperture loudspeaker.
The main object of the present invention is reached by that in a loudspeaker comprising a module having a direct radiating base electrodynamic driver (EDD) to transform an electrical signal into acoustic one at least in the middle-frequency part of the acoustic frequency range and an enclosure cabinet of said base EDD having a cone overlapping the mounting hole in the outside surface of said cabinet, according to the invention, the module is provided with an axial-symmetric acoustic reflector faced the radiating aperture of said base EDD and placed outside said enclosure cabinet and coaxially with said base EDD, wherein the distance xcex94 from the radiating aperture of the base EDD to the acoustic reflector is no less than half the radius RE of the effective area of the radiating surface of the base EDD but no more than a quarter of the maximal acoustic wavelength xcexmax in air, which is reproduced by the base EDD while the area SR of the acoustic reflector is no less than one third of and no more than the quadruple effective area SE of the radiating surface of the base EDD, that is:
0,5RExe2x89xa6xcex94xe2x89xa60,25xcexmax,xe2x80x83xe2x80x83(1)
xe2x80x83SR=(⅓÷4)SE.xe2x80x83xe2x80x83(2)
To get the most uniformity of the acoustic field in a comfort insonification zone, specifically in a comfort insonification plane (that is in the plane where presence of listener heads is supposed), the claimed loudspeaker is disposed in a room so that the base EDD axis would be normal to the plane of comfort insonification while this plane would intersect said axis between the base EDD and its acoustic reflector. So, if a room subject to insonification has a horizontal floor (for example, a dancing hall or a fashion demonstration hall), the axis of the base EDD is located vertically while the height of the loudspeaker placing corresponds to the position of listeners heads. When a room floor is slanted, the axis of the base EDD of the loudspeaker module is located perpendicularly to the plane of the floor room envelope. If a room subject to insonification has a ceiling, the base EDD is essentially faced upward while the acoustic reflector is placed above the base EDD. When the insonification is being performed in an unclosed space, the base EDD is faced downwards (to a floor) while the acoustic reflector is placed under the base EDD.
Further, according to the invention, the loudspeaker module may be provided with at least one high-frequency EDD (hereinafter HF EDD) which may be installed coaxially to the base EDD. The coaxial HF EDD and base EDD may be placed both unidirectionally and counterdirectionally. When the HF EDD and base EDD are placed counterdirectionally, the distance xcex94H between their radiating apertures is no less than radius REH of the effective area of the HF EDD radiating surface but no more than the distance xcex94 from the radiating aperture of the base EDD to the acoustic reflector, that is:
REHxe2x89xa6xcex94Hxe2x89xa6xcex94.xe2x80x83xe2x80x83(3)
One of the HF EDD may be installed coaxially and unidirectionally with the base EDD behind the backside of the acoustic reflector.
The above-mentioned placing the HF EDD (coaxially with the base EDD) assists in providing the most uniformity (non-directivity) of the resulting loudspeaker radiation.
If it is necessary to provide radiation directivity, the axis at least one of the HF EDD, according to the invention, is normal to the axis of the base EDD.
Further, the module of the claimed loudspeaker may be provided with a direct radiating low-frequency EDD (hereinafter LF EDD), a cone of which overlaps the mounting hole in the outside surface of an enclosure cabinet of the LF EDD, and also with an axial-symmetric low-frequency radiation acoustic reflector (hereinafter LF acoustic reflector), faced the radiating aperture of the LF EDD and placed outside the enclosure cabinet of the LF EDD and coaxially with the base EDD and LF EDD. Thus the LF EDD is placed co-axially with the base EDD. At that the distance xcex94L from the radiating aperture of the LF EDD to the LF acoustic reflector is no less than half the radius REL of the effective area of the radiating surface of the LF EDD but no more than a quarter of the maximal acoustic wavelength xcexL max in air, which is reproduced by the LF EDD while the area SRL of the LF acoustic reflector is no less than one third of and no more than the quadruple effective area SEL of the radiating surface of the LF EDD, that is:
0,5RELxe2x89xa6xcex94Lxe2x89xa60,25xcexL max,xe2x80x83xe2x80x83(4)
SRL=(⅓÷4)SEL.xe2x80x83xe2x80x83(5)
Herein, the effective area of the radiating surface of any EDD should be understood as an area of a round flat piston, the end surface of which has a volume oscillating velocity equal to the EDD volume oscillating velocity that, in turn, is equal to a surface integral of the oscillating velocity of elementary parts of the EDD cone:                                           ∫                          xe2x80x83                        S                    ⁢                                    V              →                        ⁢                          ⅆ                              S                E                                                    ,                            (        6        )            
where {right arrow over (V)}xe2x80x94the volume oscillating velocity of an elementary part of the EDD cone;
dSExe2x80x94the area of the elementary part of the cone.
Besides it should be clear that the area of one or other acoustic reflector is understood as the area of its working surface that is the surface faced the radiating aperture of the EDD corresponding to the given acoustic reflector, and only such surface is understood as the xe2x80x9cacoustic reflector surfacexe2x80x9d in the present specification.
Limits of the distances xcex94 and xcex94L are selected so as to provide a mode of the loudspeaker operation within limits of action of the travelling wave mechanism for flexural excitation waves radially extending in the cone.
Each EDD cone simultaneously acts in two ways: it serves as a radial transmission line of the axial excitation from a voice coil to all the peripheral cone surface parts, moreover the excited cone parts being moved act upon neighbour air molecules, involving them in motion. To ensure effective operation of the cone as said radial transmission line of the excitation signal, a concordance of this line is required, just as for any other transmission line, that is reflections (in this case, reflections of the flexural waves) from inevitable discontinuities should be reduced, excluded, or compensated. The distances xcex94Hxcex94L are selected such that, in the corresponding pair xe2x80x9ccone-acoustic reflectorxe2x80x9d, a reflected dynamic pressure excited by the central near-coil (in the case of a taper cone) part of the cone would come to the peripheral cone part in antiphase to the radial flexural wave propagated over the cone in this time and would quenched this wave at the cone edge thereby excluding standing waves in the cone and a multiplicity of a transformer response to specific temporary excitation.
The loudspeaker cone is a medium rigider than air but not perfectly rigid, therefore the distances xcex94 and xcex94L should be no less than half the radius of the corresponding cone (it is a condition of phase opposition of the reflected signal for a perfectly rigid cone moving as a single whole) but no more than a quarter of the corresponding wavelength xcex94L max and xcex94L max for the most non-rigid cone, the speed of flexural excitation wave propagation in which is equal to acoustic speed in air.
The area of one or other acoustic reflector, according to the invention, is selected within the limits determining the effective use of a co-oscillating undistorted part of the excited air for the reflection that would ensure, on the one hand, an approximate equality of the antiphase vector excitation products, and on the other hand, the described above quenching the flexural oscillations reflected from the discontinuities in the cone corresponding to given EDD acoustic reflector. Therefore the least area SR or SRL amounts to ⅓ from SE and SEL correspondingly (such as for a cones having large viscosity loss), and the most one should not exceed the area SE and SEL correspondingly more than four times because, if the acoustic reflector area is more, a radial-circular transmission line appears outside the effective radius of the cone. Such line acts as a Fabri-Perot resonator with all corresponding undesirable consequences. Thus, specific values of the parameters xcex94, xcex94L, SRHSRL depend on material of the cone, its configuration, thickness, density, rigidity, viscosity, and, therefore, is determined for a specific EDD.
According to the invention, LF acoustic reflector may be fixed at the backside of the enclosure cabinet of the base EDD. Particularly, the surface of said back side may be used as the LF acoustic reflector.
The surface of one or other acoustic reflector may be have flat or curved shape including convex, concave or stepped shape.
To provide a constancy of acoustic wave propagation in air and over the cone in the claimed loudspeaker, the envelope of surface parts of one or other acoustic reflector may be similar to the envelope of surface parts of the cone corresponding to given acoustic reflector wherein the scale coefficient of said similarity is in the range from minus two to plus two. The xe2x80x9cminusxe2x80x9d sign implies that the curvature of the acoustic reflector is the inverse of the cone curvature.
For the purposes of determination of the distances xcex94Hxcex94L, it is considered that the radiating aperture of the corresponding EDD is placed in a plane of fastening of the EDD cone peripheral part with the enclosure cabinet of this EDD. Here, if the surface of any acoustic reflector is non-planar, said distances xcex94hxcex94L are measured to an equivalent plane of the acoustic reflector. So, the distance from the radiating aperture of any EDD to the acoustic reflector corresponding to this EDD is substantially the distance from the plane of the EDD cone peripheral part fastening with the EDD enclosure cabinet to the equivalent plane of the acoustic reflector. A disclosure of the term xe2x80x9cequivalent planexe2x80x9d of the acoustic reflector will be given below using the drawings of FIG. 4 and 5.
If necessary, at least a part of the area of one or both of the acoustic reflectors may be perforated to decrease the Q-factor of the oscillations.
One or both of the acoustic reflector may be attached to the enclosure cabinet of the corresponding EDD by one or more ribs placed radially concerning the axis of the base EDD.
If the acoustic reflector is attached to the enclosure cabinet of the corresponding EDD by two or more said ribs, these ribs may be fastened with each other by flat or cone-shaped rings forming, together with said ribs, horn cells of a radial acoustic lens to additionally accent or correct a sound directional diagram in the vertical plane. Here the inner diameters of these rings are selected such that the rings would not overlap even in part a cross-section of an imaginary taper having a linear generatrix passing through the peripheral edges of the acoustic reflector and the cone of the corresponding EDD. This condition is required to provide an unimpeded passing the sound streaming waves from the EDD to the corresponding acoustic reflector.
Said ribs and fastening rings are mainly placed symmetrically relating to the axis of the base EDD. However, if the uniform sound propagation in all the radial directions from the base EDD axis, in other words, the radial uniformity (non-directivity) of the radiation is not required, the above-mentioned symmetrical placing of said ribs and rings is not obligatory.
When the cone of the base EDD and/or LF EDD is a cone without a dust cap, the corresponding acoustic acoustic reflector may be attached to a magnetic system core of the corresponding EDD by a central rod.
In order to increase the insonification area and/or dynamic range of sound reproduction (sound amplification), the claimed loudspeaker may be composed of even number of said modules which are placed in pairs and made according to one of the above-mentioned embodiments described in the claims attached. The base electrodynamic drivers in each module pair are placed coaxially. Here, the module pair may include both identical and different modules, the base electrodynamic drivers of which may be placed both unidirectionally and counterdirectionally.
If the base electrodynamic drivers in a module pair are faced towards each other, the distance between their acoustic reflectors is selected such that the acoustic reflector and the enclosure cabinet of one of said base electrodynamic drivers of the pair would not extend outside a cross-section of an imaginary taper having a linear generatrix passing through the peripheral edges of other acoustic reflector and the corresponding cone of other EDD. Said condition of selection of the distance between the acoustic reflectors should be met to avoid an ingress of the radiating reflected from the acoustic reflector as well as from the enclosure cabinet of one EDD of the pair to the cone of other EDD of this pair.
In the case, when a module pair is composed of identical modules, the base electrodynamic drivers of which are faced towards each other, the distance between their acoustic reflectors may be zero, then one common acoustic reflector having a two-sided work surface may be used for both base electrodynamic drivers of the pair.
If a directed radiation non-symmetrical in the vertical plane is required (when insonifying sports ground, swimming pools, big halls, stations and the like), the base electrodynamic drivers in the module pair are placed unidirectionally, wherein the distance between the acoustic reflector of the first base EDD located ahead in the direction of radiation of the base electrodynamic drivers in the pair and the enclosure cabinet of the second base EDD in the pair is selected such that the acoustic reflector and the enclosure cabinet of the second base EDD would not extend outside a cross-section of an imaginary taper having a linear generatrix passing through the peripheral edges of the acoustic reflector and the cone of the first base EDD.
The aforesaid condition of the lack of reflections from the acoustic reflector or enclosure cabinet of any given EDD to any other EDD should be met in any multimodule embodiment of the claimed loudspeaker. At the same time, in order to avoid unjustified increase of the loudspeaker overall dimensions, the distance between any acoustic reflector of one of loudspeaker modules and a structural component of other module, which said component is able to operate as a reflector, is selected as less as possible, when the mentioned acoustic reflector still overlaps the cross-section of interaction with its cone and therefore obstructs any other structural components able to affect the reflections.
Further the invention is explained by some specific embodiments of the claimed loudspeaker with reference to the drawings listed below.